1. Field of the Invention
The present invention relates to a push switch device for switching contact elements by pushing an actuation body projecting from a housing. More particularly, the present invention relates to a push switch device for actuating a contact element switching mechanism by rotating an actuating member spline coupled with a cam follower by converting the movement of an actuation body in an axial direction into the rotation of the cam follower through a latchet mechanism.
2. Description of the Related Art
Heretofore, there is known, as this type of the push switch device, a push switch device arranged such that an end of an actuation body is projected from a housing formed in a hollow structure, a first latchet tooth is formed to the other end of the actuation body as well as a second latchet tooth is formed to a cam follower disposed in the housing so as to rotate, rise and fall, and a latchet mechanism is arranged by engaging the first and second latchet teeth with each other by urging the cam follower upward by a return spring (refer to, for example, U.S. Pat. No. 4,891,476). The first latchet tooth has a plurality of ridge portions and valley portions that alternately continue along the circumferential direction of the actuation body. Likewise, the second latchet tooth has a plurality of ridge portions and valley portions that alternately continue along the circumferential direction of the cam follower. Further, a guide portion, in which guide projections and guide grooves each extending in an axial direction are disposed adjacent to each other, is formed on the inner circumferential surface of the housing, the actuation body can be moved only in a rising/falling direction by being guided by the guide portion, and a cam portion is formed to the cam follower so as to be engaged with and disengaged from the guide portion. In an non-actuated state in which the end of the actuation body project from the housing, the rotation of the cam follower is regulated by the cam portion that enters into the guide grooves as well as the first latchet tooth is engaged with the second latchet tooth at an unstable position where the apexes of the ridge portions of the first latchet tooth are slightly offset from the apexes of the ridge portions of the second latchet tooth.
In the push switch device that is schematically arranged as described above, when the actuation body projecting from the housing is pushed against the spring force of the return spring, first, the cam follower falls in a predetermined amount while its rotation is regulated by the guide portion. When the actuation body is pushed to a position at which the cam portion is released from the lower ends of the guide projections, the ridge portions of the second latchet tooth receive the spring force of the return spring and are moved to a stable position at which they are engaged with the valley portions of the first latchet tooth, thereby the cam follower is rotated by an angle slightly smaller than one half the ridge of the first and second latchet teeth. As a result, the actuating member spline coupled with the cam follower is rotated by a predetermined angle, and thus a movable contact element disposed to the actuating member slides on a plurality of stationary contact elements disposed to a wafer, thereby the contacting/departing state of the movable contact element and the respective stationary contact elements is changed. When the push force acting on the actuation body is released, the actuation body and the cam follower are caused to rise to the original positions thereof by the spring force of the return spring. However, since the cam portion is abutted against the lower ends of the guide projections and enters into the guide grooves adjacent to the guide projections while the actuation body and the cam follower are being caused to rise, the cam follower is rotated by an angle slightly larger than the one half the ridge of the first and second latchet teeth, thereby the first latchet tooth is engaged with the second latchet tooth again at the unstable position at which the apexes of the ridge portions of them are slightly offset. At the time, since the actuating member is rotated in association with the cam follower, the movable contact element slides on the respective stationary contact elements. When, however, the movable contact element is set so as to slide on a common stationary contact element by pushing and releasing the actuation body once, it is possible to output an ON/OFF signal from a terminal that is brought into electric conduction with the respective stationary contact elements by repeatedly pushing and releasing the actuation body (U.S. Pat. No. 4,891,476, pages 4 to 7, FIGS. 1 to 16).
Incidentally, in the push switch device employing the above latchet mechanism, the first latchet tooth formed to the actuation body is engaged with the second latchet tooth formed to the cam follower by the spring force of the return spring, and the phase of the first and second latchet teeth is changed by pushing and releasing the actuation body. However, noise is generated by the abutment between the first and second latchet teeth when the phase of the ridge portions of the second latchet tooth is changed to the stable position at the time the actuation button is pushed and thus the second latchet tooth is abutted against the first latchet tooth and when the ridge portions of the second latchet tooth get over the ridge portions of the first latchet tooth at the time the actuation body is released from the push force and thus the phase of the ridges of the second latchet tooth is changed to the unstable position, from which a large problem arises in that the quality of the push switch device is deteriorated.